Dust collector



May 19, 1942. G. w. KUERNER DUST COLLECTOR Filed July 27, 1940 a Rr OeTU N w m e mJ ma G ATTORNEY Patented May 19, 1.942

DUs'r coLLiic'roal George W. Kuerner, Mobile, Ala., assignor to AluminumCompany ot America, Pittsburgh, Pa., a corporation of `PennsylvaniaApplication -July 27, 1940,v Serial No. 347,902 4 claims. (ci. 34-102)This invention relates to improvements in drying materials andparticularly to improvements in the kiln drying or calcining of nelydivided materials or materials of which a portion is in .finelydivided'or dusty form.

The principal object of the present invention is to provide a method andapparatus for effecting the substantially complete drying of maphere.For this -reason,dust collectors are frequently employed between thepoint of egress of the gases from the kiln and the stack discharge. Inthecalcining of many typesof materials. the dust which is collected inthe dust collecting system is not a completely calcined product 'andrequires a separate calcination treatment usually in some special typeof apparatus because of its exterial, all or some of which is inextremely finely divided form in rotary type kilns with a minimum ofdust loss. A further object is the provision of a continuously fedrotary kiln drying system of relatively economical construction thatvwill permit the eiicient drying of material having a relatively widevariation in the percentage of ex-4 tremely line or dusty material ascompared with the coarser fraction of the material fedv to the.v dryingkiln. A still further object is the provision of a system of thedescribed type which will effect the complete drying of the extremelyfine or dusty portion of the kiln feed in the same ap paratus andsimultaneously with the coarser fraction of the kiln feed, andV whichwill maintain materials; the commonly employed apparatus consists of anelongated cylindrical shell mounted for rotation about its longitudinalaxis which is usuallyinclined from the horizontal topermit the feedingof the material to be'dried from the feed end to the discharge en'd bythe force of gravity. The drying is effected by a suitable fuel burningsystem mounted at the lower or discharge end of-the kiln, the heatedgases from which move along through the kiln opposite to the directionof the travel of the material being dried to the feed end of the kilnwhere the gases are usually collected in a suitable stack system andultimately carried off tothe air.

One of the principal problems encountered in the 'operation of kilns ofthis type arises when the material or a portion of the material to bedried is in finely divided or dusty form, because at least a portion ofthe extremely finely divided material will usually be picked up by thegases passing through the kiln and carried out through the stack system.If the finely divided material is allowed, to pass out through thestack, it not only.

constitutes in some instances a serious loss of the material beingdried, but in addition results in an undesirablev dust discharge intothe atmostremely fine nature. Obviously in calcining or dryingoperations it ls preferable to employ dust collectors of the dry type. v

If the dust from the dust collecting system is returned to the feed endof the kiln, a large portion of it will be picked up in the stack gasesand carried back to the dust collectors, giving rise to a largecirculating dust load in the system which may overload the dustcollecting apparatus and thereby diminish its efiiciency. This isparticularly true if the drying kiln is provided with litters in thefeed end of the kiln. Lifters are frequently employed in kilns of thedescribed type when -the material to be dried contains relatively largeamounts of uncombined water. and therefore tends to pack or lump in thekiln. In many kiln installations these lifters do not of necessityextend the full length of the kiln but only extend a relatively shortdistance from the feed end because the bulk of the uncombined water willbe driven off after the material has been fed a relatively shortdistance into the kiln and the material loses its tendency to pack.

still giving a substantially complete calcination Y of all of thematerial fed through the kiln. The invention may best be describedvbyreference to A the accompanying drawing, in which:

' Fig. 1 shows a drying or calcining kiln installation with a portion ofthe length of the kiln cut away;

Fig. 2 shows a longitudinal section through a portion of the kiln; and

Fig. 3 shows a cross section of the kiln taken along the lines III-IIIof Fig. 2.

In the drawing, l is the kiln shell mounted for rotation on suitablesupports 2. The kiln is provided with a stationary end closure 3 at itsdischarge end in which are mounted suitable burners or the like for theproduction of the drying gases. 'I'he end closure 3 is provided with adischarge 4 for the discharge of the dry material from the kiln, forexample onto a conveyor belt 5. The feed end of the kiln is providedwith a stationary end closure 6 which is adapted to act as a duct forthe exhaust gases after they are passed through the kiln. A conduit 'Iconnects the end'closure 6 with a suitable stack 8 which discharges inthe atmosphere. Mounted on the conduit 1 is a suitable dry dus'tcollector 9 of any wel1known type, such as a cone type dust co1- iector.A duct III is provided as a by-pass around the dust collector which maybe employed with a suitable valve system to control the recirculation ofa portion of the hot stack gases through the dust collector to maintainthe required volume through thedust collector for good collectingefciency. A fan I I, driven by a, motor I2, provides a forced draftsystem to augmentthe natural stack draft. The material to be dried isintroduced into the feed end of the kiln by any wellknown means, such asthe screw conveyor I3. The dust collected in the dust collectors is fedback into the kiln by discharge from the dust collectors through theconduit I4.

The specic kiln construction shown is provided with a heatresisting-lining I of fire brick or the like extending from thedischarge end of the kiln, at which end the kiln temperature is thehighest, through a major portion of the kiln length stopping short ofthe feed end of the kiln. Suitable lifters, such as the channels I6,extend from the feed end of the kiln to a point adjacent the end of thelining I5.

Mounted within the kiln is a circular receptacle Il having its axissubstantially coincident with the axis of the kiln and attached to thekiln shell I by braces I8. The conduit I4 from the duct collector isadapted to discharge the fine material from the dust collector throughan axially disposed opening into the receptacle I1 during rotation ofthe kiln. A plurality of boxes I9 are fixed to the interior of the kilnshell I at intervals along the kiln length in staggered relationship andon diametrically opposite sides of a plane bisecting he kiln. Each ofthe boxes I9 extends about a portion of the kiln periphery and each endof each box is adapted for communic'ation with tubular ducts, such asthe ducts 2I. The tubular ducts 2I interconnect the oppositely disposedstaggered boxes I9, and each duct in successive order along the kilnlength is oppositely inclined with respect to the kiln axis and are eachconnected with those ends of the boxes I9 which lie on the same side ofa plane through the center line of the kiln and parallel to the ducts2I. Tubular ducts 20 and 22, disposed in the same relative positionswith respect to the boxes I9 as the ducts 2l, complete a passage systemfrom the receptacle I1 to the point of discharge on or near the kilnlining? The operation of this apparatus is as follows. Material from thedust co1lector'9 is fed through the conduit I4 into the circular box I1,then through the duct 20 into one end of the box I9 nearest the feed endof the kiln. As the kiln is rotated in the direction indicated by thearrow shown in Fig. 3, the material slides through the box I9 to theopposite end of the box into which it has been introduced, and as thekiln is further rotated, it goes through one of the ducts 2I into thenext adjacent box away from the feed end of the kiln through which ittravels in the same manner as previously described into the next duct2'I. The finely divided material recovered in the dust collector isfinally discharged through the duct 22 into the kiln at a point adjacentthe kiln lining I5.

During the passage of the dust or fine material through the systemdescribed, it has practically no contact with the gases passing throughthe kiln, and therefore during this period it cannotl be picked up bythe kiln gases. By thus limiting the period of contact with the kilngases, less of the finely divided material is picked up by the kilngases. The conduit system receives some heat from the kiln gases andserves to further dry the material being fed therethrough. The dust'lpicked up by the gases is further reduced by discharging the finelydivided material from the dust collector into the kiln at a point pastthe kiln lifters.

It has been found that the above described system of introducing thefinely divided material from the dust collectors into the kiln isgreatly effective in reducing the circulating dust load in the kiln anddust collector system. As the material collected in the dust collectoris fed into the kiln with the co'arser material passing through thekiln, the discharge from the kiln will contain substantially the sameratio of extremely fine material to coarse material as the materialintroduced at the 'feed end. This is of great advantage as it avoids thenecessity for a separate mixing operation in those frequent instanceswhen the material is specified to have a uniform ratio of fine to coarsematerial. The specific apparatus described is simple in construction andutilizes the kiln drive to move the fine material from the dustcollector from the feed end of the kiln to the point of discharge Withinthe kiln.

While the invention has been described in connection with the operationof a specific apparatus, it is to-be understood that there is nointention of excluding any equivalent or obvious variation of theinvention as set forth in the appended claims.

I claim:

1. Apparatus for drying material comprising a kiln adapted for thepassage of material therethrough, means for feeding the material to bedried into one end of said kiln, means at the opposite end of the kilnfor discharging dried material, means at the discharge end of said kilnfor supplying drying gases for passage through said kiln in contact withthe material being dried in a direction opposite to the movement of thematerial, a dust collector adapted to recover the fine material carriedby the gases leaving the feed end of the kiln, and means comprising apassage system located Within the kiln adapted to receive the finematerial recovered in the dust collector andconvey said material fromthe feed end of the kiln through a substantial portion of the kilnlength while maintaining said material substantially out of contact withthe drying gases, said passage system being adapted to discharge saidfine material within the kiln at a point remote from the feed end toprovide a reduced period of contact of said ne material with the dryinggases.

2. Apparatus for drying material comprising a rotary kiln adapted forthe passage of material therethrough, means for'feeding the material tobe dried into one end of said kiln, means at the opposite end of thekiln for discharging dried material, means at the discharge end of saidkiln for supplying drying gases for passage through said kiln in contactwith the material being dried in a direction opposite to the movement ofthe material, a dust collector adapted to recover the fine materialcarried bythe gases leaving the feed end of the kiln, and meanscomprising a passage system located within the kiln adapted to receivethe ne material recovered in the dust collector and convey said materialby the rotation of the kiln from the feed end of the kiln through asubstantial portion of the kiln length while maintaining said materialsubstantially out of contact with the drying gases, said passage systembeing adapted to discharge said fine material within the kiln at a pointremote from the feed end to provide a reduced period of contact of saidne material with the drying gases.

3. Apparatus for drying material comprising a rotary kiln adapted forthe passage of material therethrough, means for feeding the material tobe dried into one end of said kiln, means at the opposite en d of thekiln for discharging dried material, a plurality of lifters located nearthe feed end of said kiln, means at the discharge end of said kiln forsupplying drying gases for passage through said kiln in contact .withthe material being dried in a direction opposite to the movement of thematerial, a dust collector adapted torecover the fine material carriedby the gases leaving the feed end of the kiln, and means comprising apassage system located within the kiln adapted to receive the nematerial recovered in the dust collector and convey said material fromthe feed end of the kiln through a substantial portion of the kilnlength while maintaining said material substantially out of contact withthe drying gases, said passage system being adapted to discharge said nematerial Within the kiln at a point remote from the feed end and beyondsaid lifters to provide a reduced period of contact of said ne materialwith the drying gases.

4. Apparatus for drying material comprising a kiln adapted for thepassage of material therethrough, means for feeding the material to bedried into one end of said kiln, means at the opposite end of the kilnfor discharging dried material, means at the discharge end of said kilnfor supplying drying gases for passage through said kiln in contact withthe material being dried in a direction opposite to the movement of thematerial, a dust collector adapted to recover the fine material carriedby the gases leaving the feed end of the kiln, and means comprising `apassage system located within the kiln adapted to receive the finematerial recovered in the dust collector and convey said material fromthe feed end of the kiln through a substantial portion of the kilnlength while maintaining said material substantially out of contact withthe drying gases, said passage system being adapted to discharge saidfine material within the kiln and adjacent the kiln lining at a lpointremote from the feed end to provide a reduced period of contact of saidfine material with the drying gases.

, GEORGE W. KUERNER.

